How to add Dry knob to a Big Muff?

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Post by cocnut »

Hi! I'm trying to modify a Big Muff circuit adding clean signal blend. I've tried a few solutions but I'm not quite satisfied with any of them.
Initial idea was to add an input buffer (non-inverting op-amp) and split the signal into two patches also increasing input impedance significantly. I also wanted to boost clean signal a bit to make it more audible when the dry knob is set past 12 o clock. I've tried something like that (screenshot). What do you guys think? Maybe there is a good solution but I can't find it :) thanks in advance!


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Post by jonfoote »

this is how ehx did it for the bass big muff

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Post by stolen »


This looks like it'll work poorly to be honest; here's what we notice:

- Aside from C15 the wet source is very stiff, so R27 doesn't really stand a chance to change the output. Adding a resistor (also 27k) in series with C15 will fix that and give you a proper ~50/50 mix (variation courtesy of output impedance of RV5).
- If it's a standard muff the output is ground referenced, and while R24 will pull it up a tiiiiiiiny bit it'll be nowhere near proper biasing to let U2A work without clipping. Add a series cap to decouple that and it should work.
- R23 and R26 do nothing*, R28 does effectively nothing

If it was us we'd omit U2A entirely for simplicity; this will introduce interaction between volume knobs depending on the ratio of their resistances and R27 and its atm nonexisting counterpart, but you already kinda got that with dry volume. There's the option to modify the topology to suppress that entirely: Keep U2A, but hook up dry volume after U1A and go into U1B from there, so that the mixer sees stiff sources on both sides. This will also would result in hot signals that would otherwise clip U1B not doing so at reduced volume levels.

Hope this helps!

*they do bias the OPAs' output stages ever so slightly into class A but we doubt that it makes any difference

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Post by jw23mind »

Instead of a "separate" clean-blend, I like to put a resistor in series with the clipping diodes; had luck with values around 2-3kOhm on a russian muff. Too high of a value and the the "cleans" start to poke through the distortion too much, sounding like a separate signal; but get it right and it makes for a more lively, dynamic fuzz.

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Post by Lukasen »

I think it's called warping control - putting a 1k resistor in series with a 10k pot as a variable resistor before clipping. It's a simple solution.

For a dry/wet signal mix, I would first try spliter-blend from runoffgroove: and then figure out what works and what doesn't work (or add additional buffers to separate the signal).

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Post by Ben N »

Assuming everything else stays more or less the same, you have an unused opamp (U2B). Why not use it as a virtual ground mixer?

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